It should be easy for anyone to set up an Internet radio station and it should be easy for anyone to listen to it. This site attempts to promote this principle by providing a directory of stations streaming using open codecs. Well known codecs include MP3 and WMA. These are proprietary, with restrictions on use and modification.
Open codecs do not require licensing and may be improved upon by anyone with relevant skills. This benefits developers, who can pass improvements in audio quality and software on to the broadcaster and listener.
Radio has, for years, been constrained by licensing of the airwaves. On the Internet, there's no need for such restrictions, but radio is still facing attacks from many fronts. The most onerous of these is the licence fees levied by the 'industry bodies' in the US. Other threats include the proprietary nature of some technology involved in production, transmission and reception.
The amount of raw audio data stored a compact disc is large enough that most people's Internet connections are too slow to allow streaming the music to them in 'real time'. For downloading audio to listen to later, this isn't such a problem, but for radio, people want to be able to listen 'live'. Audio compression allows this to happen.
The audio codec which everyone has heard of is MP3. It is a proprietary, patented, codec. Anyone who makes a program or device which plays or records MP3 is required to pay licence fees. These fees can be prohibitively expensive for developers - especially those who do not profit from the software they produce. Those who develop free software are still liable to pay licence fees.
Most players support MP3 simply because it's the most popular format: people expect to be able to play MP3s. The popularity of the format, however, has nothing to do with its technical strengths and seems to be mainly due to the laziness and lack of intelligence of the media.
There are many audio codecs, but MP3 was the first word on the lips of various reporters and others didn't bother to investigate other formats, or, because they didn't really understand was MP3 was, didn't even consider that there could be alternatives. If they did look into alternatives, they didn't understand enough to talk about them with confidence, so they took the easy route, even referring to competing formats as 'MP3', ostensibly to avoid confusing the public, but in reality to avoid confusing the reporters.
The alternative audio codecs are not as alternative as you might expect. Apple's iPod, in addition (and in preference) to MP3, supports AAC, which is technically (and practically) vastly superior to MP3. Apple encourage users to choose AAC by making it the default codec used by iTunes. When you buy a track from the iTunes store, you get AAC. When you 'rip' tunes from a CD to listen to in iTunes or on your iPod, iTunes encodes them in AAC.
The technical differences between audio codecs are many. This site, however, is most concerned with the openness of formats, so will leave the interested reader to investigate.
This site considers an audio codec open if it is relatively free from restrictions on its use. Requirement to obtain a licence to use the codec is not acceptable, especially if a licence fee is charged. Attempts to require licensing of alternative implementations or competitive formats using similar ideas are also unacceptable.
Currently the only codec which is widely used for audio streams and meets the requirements is Vorbis. This site, therefore, links only to Ogg Vorbis streams. It may be of interest that Wikipedia currently uses Ogg Vorbis for all sound recordings, for reasons similar to those given on this site.